Vee belt manufacture

ABSTRACT

A method of treating a conventional vee-belt (having a polyester reinforcement) to stabilize the belt at a required nominal length includes the steps of pre-vulcanizing the otherwise completed belt on a heating drum around which the vee-belt is passed without tension being applied. The belt is prepared for vulcanization under tension so as to eliminate shrinkage caused by the pre-vulcanization step and bring the belt back to its original length. Subsequently the belt is stretched over two rollers under a standard load and when the required length is achieved, is given a permanent set by immediate cooling.

United States Patent [1 1 1111 3,761,558

Hnatek Sept. 25, 1973 [54] VEE BELT MANUF CTURE 3,216.18? ll/l965Chantry 57/140 1161 Inventor hawk, weinbergstrasse 33232133; 311323$212,111:1::.....................;;::1523/338 l7, Hoxter/Weser, Germany[22] Filed: June 8, 1971 Primary Examiner-Donald J. Arnold App]. No.:151,099

Related US. Application Data [63] Continuation-impart of Ser. No.783,076, Oct. 14,

1968, abandoned.

[52] US. Cl 264/231, 264/DIG. 59, 264/290, 264/347 [51] Int. Cl B29h7/22 [58] Field of Search 264/231, 290, 347, 264/DIG. 59

[56] References Cited UNITED STATES PATENTS 3,233,020 2/1966 Meumann264/347 X 3,469,001 9/1969 Keefe 264/290 2,325,204 7/1943 Kilbern264/23] 3.107,|40 l0/l963 Kurzke 264/290 +lU U +lU AssistantExaminerRichard R. Kucia Att0rneyMason, Mason & Albright 5 7 ABSTRACT Amethod of treating a conventional vee-belt (having a polyesterreinforcement) to stabilize the belt at a required nominal lengthincludes the steps of prevulcanizing the otherwise completed belt on aheating drum around which the vee-belt is passed without tension beingapplied. The belt is prepared for vulcanization under tension so as toeliminate shrinkage caused by the pre-vulcanization step and bring thebelt back to its original length. Subsequently the belt is stretchedover two rollers under a standard load and when the required length isachieved, is given a permanent set by immediate cooling.

5 Claims, 5 Drawing Figures PATENTED SEPZS I975 SHEET 1 ur 4 INVENTOR e:A RNA-rem PATENTEDSEPZSIQB 3.761 558 TEMPERATURE "C l l I I I ISHR/NKAGE A FIG.

INVENTOR JosaF A. HNATEK VEE BELT MANUFACTURE CROSS-REFERENCE TO RELATEDAPPLICATION This application is a ccihtinuation-impart application toapplication Ser. No. 783,076 filed Oct. 14, 1968 for Vee-beltmanufacture, method and (now abandoned).

BACKGROUND OF THE INVENTION The invention relates to a method ofproducing stabilized Vee-belts having a rubber body and internalreinforcements of polyester fiber cord.

The tensile member subject to elastic contraction is a polyestermaterial yarn, thread or tape having the following characteristics: Whena tensile member made of one of these materials is subjected to heatingto between 100 and 180 C. and is not securely gripped, it contractslengthwise to some extent (1 to 7 percent, according to the nature ofthe tensile member concerned). When cold, the polyester materialexhibits only its property of elastic elongation.

The invention turns this effect to account for length stabilization, thebelt being secured in the hot condition at the desired length, whichlies between the contraction percentages.

After cooling, contraction is no longer possible, for polyester isunaffected by moisture.

A Vee-belt incorporating a tensile component made of a material that isaffected by moisture, such as rayon, for example, undergoes longitudinalshrinkage by the absorption of moisture during storage and isaccordingly unsuitable for the proposed method.

It is general knowledge that conventional Vee-belt drives are composedof several such belts combined to form a set and hence that their lengthmeasurements must be accurate in order to avoid excess loading of theshorter belt or belts. The total tolerance acceptable in such drives is0.25 percent of the nominal length of the belts; and in many instancesonly half that figure is permissible.

It has already been proposed in the US. Pat. No. 2,325,204 to Kilborn tovulcanize rubber Vee-belts in a side-by-side arrangement on a pair ofappropriately grooved drums. Heating of the belts to effectvulcanization is produced by the passage of a hot medium throughpassages within the grooved drums and, during vulcanization a stretchingtension is applied to the belts by means of a hydraulic motor whichforces the two drums apart. At the same time those parts of the beltswhich are at any given time in engagement with the grooves of the drumsare also subjected to a pressure acting radially inwardly by clamp armswhich engage the outer surfaces of the belts over approximately 180of-arc at each drum.

The belts which are to be treated by the process described in this priorspecification have an unspecified reinforcement and there is noindication that any problem arises with regard to shrinkage of the beltsor the need to stabilize the belts at a predetermined dimension.

The prior specification also discloses a method of vulcanizing anendless rubber Vee-belt comprising supporting the belt at spaced pointson its inner periphery, moving the supporting points apart to stretchthe material, limiting the movement apart of the support points byflexibly and inextensibly confining the outer periphery of the belt whenthe movement apart of the support points has brought the material lengthto exactly that desired, subjecting the inner and outer peripheries ofthe belt to the action of vulcanizing heat, and moving the belt along anendless path during the application of the vulcanizing heat.

The previously proposed apparatus and method were developed prior to thediscovery of polyester fibers and hence neither apparatus nor method arecapable of taking into account the shrinkage property of a rubberVee-belt having a reinforcing or tensile member of polyester fiber.

An object of the present invention is to provide a method of producing aVee-belt of exact dimensions and which is dimensionally stable in useapart from normal elastic stretching under load.

SUMMARY OF THE INVENTION According to the present invention, there isprovided in a method for forming a plurality of Vee-belts of uniformlength, each belt including a tensile member of elastically-contractilepolyester material which contracts on heating, the improvementcomprising the steps of subjecting each said Vee-belt, after passagethrough vulcanizing apparatus in unstressed condition in which initialvulcanization is effected, to a vulcanizing step whilst tensioned by anamount which offsets the contraction of the tensile member resultingfrom the initial vulcanizing step, immediately thereafter placing thebelt under a standard load, stretching the belt by an amount to bring itto the nominal length, and cooling the belt to stabilize it at thenominal length.

By this method, the behavior of the tensile member or otherreinforcement of the Vee-belt as regards elastic contraction is socontrolled that belts of equal, and stable length are produced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows part of the vulcanizingunit in equipment for putting the method into practice;

FIG. 2 shows a portion of the unit illustrated in FIG.

FIG. 3 shows part of a stretching device forming part of the apparatus;

FIG. 4 is a graph in which temperature is plotted against shrinkage inpercent for a particular polyester fiber; and

FIG. 5 is a graph of time in minutes plotted against shrinkage inpercent for the same polyester as that of FIG. 4, at a temperature of C.and a load of 250 grams.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, agrooved heating drum 1 of the vulcanizing unit, co-operates with aroller 2 that can be adjusted and locked in the direction in which aconventional Vee-belt 3 with a polyester reinforcing member to betreated is tensioned. One or more Veebelts 3 pass around the heatingdrum 1 operating for example at 150 C. and the roller 2. The tensilemember of the Vee-belt is in polyester of known type and has aconventional fabric cover and an example thereof will be describedhereinafter, in detail.

Also slowly passing around the heating drum 1 is a belt 4, which can betensioned by means of an adjustable roller 5. This belt 4 is also ledaround guide rollers 6, mounted on pivotally connected arms 7, which areheld together by a pair of straps 8. The drum rotates at a rate of onerevolution for every ten to eighteen minutes. The vulcanization time isdependent upon the width and height of the belt and of the rubber mix.

While the Vee-belt, or belts for example fifteen if the drum has acorresponding number of peripheral grooves, arranged side-by-side, ispassing round for the first time, pre-vulcanization takes place with thebelt or belts substantially unstressed to enable the thermal contractionof the tensile member to take full effect. Thus, the tensile memberwithin the Vee-belt is shortened by the distance A (FIG. 2) inconsequence of the vulcanizing process.

Next, a small amount of tension having been applied by movement of thetensioning roller 2, the belt 3 is subjected to a second stage ofvulcanization while under tension, until the contraction of the belt hasbeen offset as a result of this stretching process. The secondvulcanizaton is therefore ended upon the original starting length havingbeen reached.

The hot Vee-belt 3 is thereupon removed from the apparatus and at oncepassed on a convenient holder to a stretching device (FIG. 3), which hastwo rollers 9 and 10, to take the belt 3. One of these rollers 10, canbe adjusted and locked in the direction in which the belt 3 istensioned. This roller 10 is mounted with freedom to rotate in atensioning carriage 11, which can be moved and locked in position bymeans of a tensioning wheel 12.

For coarse adjustment, a running rail 13 below the carriage 11 containsrecesses 13a, in which a screw 14 can be selectively engaged.

The roller 9 is mounted with freedom to rotate in a carriage alsomounted on the rail 13, to which a tensile standard load 16 can beconnected. This standard loading is laid down precisely, for any givenbelt crosssection, in German DIN Standards 2215', 7753 sheet 1 and 7753sheet 3.

For ease of reference the following extract is given from theseStandards:

Measurement of the belt length The effective length L or the length Lare derived as follows: The belt is fitted according to FIG. 6 over twoequal sized measuring Vee-belt pulleys, the groove form and the valuesof which are respectively set out in FIG. 7 and Table 2. The movablemeasuring pulley is so loaded that the measuring force Q acts on thebelt. In order to ensure proper seating of the belt in the grooves, thepulleys are rotated under load so that before the measurement of theaxis spacing e at least three rotations have been completed. Theeffective length L,,, is derived from twice the axis spacing e plus theeffective periphery U of the measuring Vee-belt pulley, or from theequation. The outer length L is given For belt section SPZzL L, 13

SPAzL, L +18 SPBzL L,,, 22

SPC:L,, L 30 l9: L L 25 TABLE 2.

Measurements of Vee-belt pulleys and measuring force ExplanationsMeasuring force Q" Dimensions of Vee-belt pulleys kilograms Belteffective Effective Outer Effective Groove Section circumfediameterdiamwidth Depth rence 1,, eter b f U 0.05 d, minim- SPZ 300 95.49 8.5 ll36 SPA 450 143.24 149 11.0 14 56 SP8 600 190.99 198 I40 17 90 SPC 1000318.31 328 19.0 24 150 I9 800 254.65 263 16.0 20 120 5. The value isrecommended by ISO.

The sections SPZ, SPA and SPB correspond to ISO- recommendations.

R 459 Grooved pulleys for narrow Vee-belts;

R 460 Lengths of narrow Vee-belts.

Other details of the dimensions and characteristics of standardVee-belts are also given in these DIN Standards.

The movement of the carriage 15 is limited in one direction by a stop 17secured to the rail 13.

Connected to the rollers 9 and 10 are gauge marks 18 and 19respectively, which operate in conjunction with the correspondingmeasurement scales 20 and 21.

Between the two rollers 9 and 10 is a cooling device 22, whichstabilizes the Vee-belt or belts 3.

The vee-belt set made up of the individual belts 3 is fitted while hotover the rollers 9 and 10 of the stretching device (FIG. 3), which canbe set in such a way as to bring the gauge mark 18 opposite zero, whilethe gauge mark 19 indicates the nominal length of for example 2,000 mm.,on the scale 21. Next, a drive is applied to one or both of the rollers9 and 10, so that the belt 3 moves in the sense of the arrow. Then thebelt is briefly subjected while hot to the tensile standard load 16 andthen relieved of the loading. When, upon removal of the load, the gaugemark 18 reaches the measurement mark zero on the scale 20, the length ofthe belt is at its predetermined nominal value, so that the coolingdevice 22 can be brought into action to stabilize it at that value.Alternatively, the cooling device 22 lies within the boundary of theVee-belts and is ar ranged to direct cooling air outwardly through anumber of jet nozzles. The air flow is approximately 10 cubic meters perminute at a pressure of millimeters water gauge. The cooling air ispreferably at a temperature of from 8 to 15 C. and cools the belts toapproximately 50 C. in a time of from 6 to 8 minutes. Further cooling isunnecessary since substantially no further shrinkage occurs at lowertemperatures.

Should the gauge mark 18 reach only the scale reading 8, the roller 10in FIG. 3 is moved to the right until the gauge mark 19 indicates thevalue +2,008 (millimeters) on the length scale.

On the other hand, if the gauge mark 18 should move out as far as themeasurement value +4 (millimeters), the roller 10 should not be moved,so that the gauge mark 19 stays at the reading 2,000 (millimeters) onthe scale 21. Then, when this is followed by the cooling action, thebelt 3 will contract precisely to the set measurement.

After cooling, the standard loading 16 is again applied by way of check,to verify that the length of the belt 3 is correct. The gauge mark 18will then be seen to move the zero reading on the scale 20.

The invention is applicable to all conventional Veebelts having apolyester tensile member or other reinforcement which contracts onheating. Such belts are generally based on a standard vehicle tirerubber mix such as natural rubber, Buna and Neoprene (Registered TradeMark) containing fillers such as carbon black, chalk and kaolin, ageingand fatigue retarders and a vulcanization accelerator such as sulfur.

The reinforcement takes the form of a polyester fiber cord. A polyesterfiber may be defined as a long-chain synthetic polymer generallyproduced as a condensation product from the reaction of ethylene glycoland terephthalic acid or its derivatives and which has been formed intoa textile fiber or filament.

To form the yarn a melted mass of the condensation product is spun at275 to 290 C. and is then stretched slightly. The yarn made in thismanner is twisted as a multi-filament and then transformed into a cord,which has for example the dimensions 1,000 Denier/ 3 X 3 or Nm p.3 X 4.This yarn is marketed under the Registered Trade Mark Diolen 1625 andhas the following properties: Breaking load 88.5 kg; stretch at 30 kg.3.4 percent; stretch at 50 kg. 6.5 percent; extension at rupture 10.4percent; weight per 100 meters 145.2 grams. This cord is then dipped inrubber. The dipping compound used is a mixture of vinyl pyridine latex(Gentax) and resorcin formaldehyde. Other examples of suitable fibersare Trevira" GPA'produced by Farbewerke Hoechst, Germany, Terlenka 760produced by Algemeene Kunst. Unie. Holland, and Dacron by Du Pont in theUnited States of America. Shrinkage tests have been carried out oncertain of these polyester fibers and it has been shown that as in thespecific example given hereinafter the percentage shrinkage at 150 C. isfrom 3 to 4 percent. Clearly, this degree of thermal shrinkage is notpermissible in vee-belts and the method in accordance with the inventionovercomes this disadvantage by reducing, in the finished vee-belts, thethermal shrinkage substantially to zero. Examples of suitable materialsare disclosed in US. Pat. No. 3,216,187.

The cord is then subjected to the second heat treatment, which iscarried out at 200 C.

Every Vee-belt consists of three rubber mixes, namely a carcass mixturesuch as is used in the construction of motor vehicle tires and whichencases the dipped fibers and a rubberized textile covering. The carcassmixture has for example the following composition:

Elastomer (natural rubber, Buna, Neoprene) 100 parts Fillers, carbonblack of SRF type 45 parts Zinc Oxide 5 parts Softener oils 3-5 partsAnti-ageing and fatigue agents 2-3 parts Sulfur and accelerators,according to the type of elastomer 14 parts Such a mixture has ahardness depending on the required rate of vulcanization of theoperating apparatus for example 65 Shore A. p

The rubber cushion on whichthe cord rests when in use and passing overpulleys has for example a hardness of 80 Shore A, and the formula forthe rubber mixture is as follows:

Elastomer (natural rubber, Buna. Neoprene) 100 parts Fillers, oil carbonblack, chalk, kaolin 90-100 parts Zinc oxide 5 parts Softener oils partsAnti-ageing and fatigue agents 2-3 parts Sulfur and accelerators,according to the type of elastomer bers. The rubber layer on both sidesof the textile material, which can be applied to the rubber roller bymeans of a rubber solution or friction (solid mixture) has the followingcomposition:

Elastomer (natural rubber, Buna,Neoprene) parts Fillers, gas carbonblack of type HAF, also electrically-conducting carbon black 45 partsZinc oxide 5-10 parts Magnesium oxide 5-10 parts Softener oils(according to processing as solution or solid mixture) 5-25 partsAnti-ageing and anti-fatigue agents l-3 parts Accelerators (according toelastomer and vulcanizing time required) l-4 parts Such a mixture has a70 Shore A hardness.

The temperature ranges for the pre-vulcanization are adapted to therubber mix to be vulcanized, and have to be matched to the peripheralspeed of the rotating drum. The preferred temperatures of the surface ofthe vulcanizing drum, that is at the vee grooves for the belts between145 and 158 C. and are coupled with the time of rotation and theaccelerators of the rubber mix; the temperatures therefore depend on therate of vulcanizing of the elastomer mix. A pre-set temperature is keptconstant throughout the vulcanizing process (i.e., preand secondaryvulcanizing or 1st and 2nd vulcanization). The cords of the Vec-beltsare heated in dependence upon thermal conductivity of the encasingrubber mix, and through the degree of cord shrinkage it is possible todetermine according to shrinkage diagram of FIG. 4 the percentage of theshrinkage path.

A shrinkage force in kilogrammes corresponds to this shrinkagepercentage. If it is desired to restore the Veebelt to its originallength with the same heat action, it is only possible with the action ofheat, the shrinkage force has to be calculated for each Vee-belt onretightening. It is found in practice that about twice the shrinkageforce has to be used to stretch the Vee-belt in the second vulcanizingcycle, in order to obtain the same extension of the cord throughout thelength of the Vee-belt.

if the temperature remains constant during the second vulcanization, therotational speed can be the same as that of the first cycle, but canalso be up to five times faster, depending upon the height of theVee-belt section.

An example of the process in accordance with the invention will now bedescribed as applied to Vee-belts of particular size.

A set of Vee-belts consisting of, for example, 15 Veebelts of section,outer width 17 millimeters by height 1 1 millimeters, 3,000 millimetersinternal length is mounted on the rotary vulcanizing apparatus and thetension drum 9 is tightened by means of a predetermined weight 16 whichcan be calculated from the following values: ln a Vee-belt of the abovesection 17 X 11 there are nine cords of the structure Nm 9/3 X 3. Thisproduces for the 15 Vee-belts cords and there will thus be 270 cords forupper and lower runs. The fundamental load in the shrinkage tests of thecord used is given as 200 grams/cord. Thus for all the belts apre-stress of 270 X 200 54 kg. was chosen which, in practice means 60kilograms owing to frictional losses.

The first vulcanization is now carried out substantially without stresssince the load of 60 kilograms for the Vee-beltsproduces substantiallyno elongation.

The vulcanizing drum rotates very slowly, namely at a peripheral speedof 0.1 meter per minute. This speed is matched to the vulcanizing curveof the rubber mix at a temperature of 158 C. The temperature of thegrooves of the vulcanizing drum is regulated accurately by thermostatswith electrical heating.

The Vee-belt set enters the vulcanizing drum at the bottom and at thetop the hot vee-belts emerge. The hot prevulcanized Vee-belt thatemerges shrinks according to the temperature attained by the cord (seeFIG. 4). In this example the tension drum 2 will move by an axialdistance of 36 millimeters in relation to the vulcanizing drum; thisresults in a belt length of 2,928 millimeters and a shrinkage value of36 X 2 X 100/3000 2.4 percent of the length.= 72 millimeters.

When the first revolution without tension is completed (this revolutioncan only be carried out free from tension, for in fixing the Vee-belts,the cord threads would contract in the softened sub-structure of theVee-belts, and thus yield only faulty products), a cord position isattained which lies perfectly in the Veebelt, considered incross-section.

In the second vulcanizing cycle a load of 1,000 kilograms is applied;this can be done without risk of damage, because the sub-structure ofthe Vee-belt is vulcanized with the upper structure (i.e., iselastically solid). This 1,000 kilogram tensile force is calculated fromthe shrinkage force per cord thread with 2.4 percent shrinkage. Thisforce is calculated at 3.7 kg per cord thread.

270 cord threads X 3.7 kilograms grammes.

At the end of the second revolution, which is carried out at a speed ofthe vulcanizing drum between 0.10 and 0.50 meter per minute (in thiscase 0.30 meter per minute at the same vulcanizing drum temperature ofl58 C.), the initial length of 3,000 millimeters is again attained.

If the Vee-belt set were to be taken hot from the apparatus, i.e.,without further treatment, the hot part of the Vee-belt set which isabout 3,000 millimeters long, i.e., in this case about 1,400 millimeterslong after the residual temperature would shrink 1,400 X 2.4 percent 33millimeters. The Vee-belt set would therefore attain a dimension of2,967 millimeters after cooling. The partly hot vee-belt set is thenrapidly removed by means of a convenient device from the vulcanizingapparatus and placed in the second apparatus (FIG. 3) which consists oftwo grooved drums. One grooved drum can be adjusted along a millimeterscale to the desired length of vee-belt (3,000 millimeters) and fixed.The other grooved drum only moves 4-5 millimeters in the axial distanceaccording to the expansion diagram of the cord, during the measuringprocess. In this case, with the standard load of 36 kilograms determinedby German Standard DIN 2215, with the load on the set of 15 X 36kilograms 540 kilograms there is an axial distance of barely 3millimeters.

1,000 kilo- If the vee-belts, under this standard load, attain the zeromark, after 3 millimeters expansion of the whole set, because they are,in part, still hot, they become cooled in the regularly recurringmeasuring rhythm. After cooling, the vee-belts are removed from theapparatus; they are now capable of being stored with a constant length.When measured individually they display in relation to one another nogreater tolerance than i 2 mm in length.

Length of belt in this example is therefore 2,998 3,002 millimeters.

German Standard DIN 2215 permits a batch tolerance of: 4 millimeters,i.e., 2,9963,004 mm.

Accordingly, with the method of manufacture which used the heat ofvulcanizing for stabilizing the length by means of standard load, thevee-belts are much more accurate than is prescribed in the GermanStandard DIN sheet 2215. Even with a belt length of for example 17 X5,000 millimeters, Vee-belts in accordance with the invention can keepto a tolerance ofi 2 millimeters, which compared with DIN 2215 at 5,000millimeters is much more accurate, by i 6.25 mm. Hence it is possible todeliver sets from stock without checking the measurements.

1 claim:

1. In a method for forming a plurality of vee-belts of uniform length,each belt including a tensile member of elastically-contractilepolyester material which contracts on heating, the improvementcomprising the steps of subjecting each said Vee-belt, after passagethrough thermal vulcanizing apparatus in an unstressed condition inwhich initial vulcanization is effected, to a thermal vulcanizing stepwhile tensioned by an amount which offsets the contraction of thetensile member resulting from the initial vulcanizing step, immediatelythereafter placing the belt under a load which is sufficient to preventits contraction due to cooling and cause a slow expansion of the beltwhile still hot, stretching the belt by an amount to bring it to itsdesired length, and cooling the belt to stabilize it at the said desiredlength.

2. In a method for bringing an initially partially, thermally-vulcanizedvee-belt to its desired length, said vee-belt including a tensile memberof polyester material which contracts elastically with increasingtemperature, the steps of further thermally-vulcanizing thepartially-vulcanized belt while tensioned for a time sufficient tocompensate for the contraction caused by the initial partialthermal-vulcanization, and immediately placing the hot belt under atension caused by a load sufficient to prevent its contraction due tocooling and cause a slow expansion of the belt while still hot in orderto stretch the belt to bring it to its desired, length, and cooling thebelt to give a permanent set.

3. A method according to claim 1, wherein the vulcanization in theunstretched conditon takes place at C.

4. In a method for producing a plurality of Vee-belts of uniform length,each belt including a tensile member of elastically-contractilepolyester produced as a condensation product from the reaction ofethylene glycol and a substance selected from terephthalic acid andderivatives thereof and which has been formed into a textile filament,each filament being liable to contract on heating, embedded in a vehicletire rubber mix, the improvement comprising the steps of subjecting eachsaid Vee-belt to an initial thermal vulcanization while the belts are inmotion around spaced pulleys and substantially free of tension,subjecting each said Vee-belt to further thermal vulcanization while thebelts are in motion around spaced pullys and under a tension such thaton completion of the further vulcanization the contraction produced bythe initial vulcanization has been offset, immediately thereafterplacing each hot belt under a load for its dimensions which issufficient to prevent contraction from the effects of cooling and allowa slow expansion of each belt while still hot, stretching each belt byan amount to bring it to the precise length which is desired, andimmediately cooling the belts to room temperature to stabilize them atthe said desired length.

5. A method of forming a plurality of vee-belts of uniform length, eachbelt composed of rubber material which encases a tensile member ofelasticallycontractile polyester material having the physicalcharacteristic of contracting on heating, the method comprising thesteps of:

Subjecting said belts to a first thermal vulcanizing cycle in anunstressed conditon whereby said rubber material of each belt isvulcanized with its tensile member located therein in its desiredposition and each said belt shrinks to less than its original lengthfrom the contraction of its tensile member;

Subjecting said belts to a second thermal vulcanizing cycle whileapplying sufficient tensile force thereto whereby said belts attaintheir original length in this second cycle;

While said belts are still hot, rotating same under a tension sufficientto prevent their contraction while cooling and cause slow expansion ofthe belts while still hot, and at the same time continually measuringthe length of said belts; and

When said belts attain their original length, cooling said belts whilecontinuing to rotate same; whereby each said belt has a permanent lengthwithin a tolerance of not greater than 0.067 percent variance of itsoriginal length.

2. In a method for bringing an initially partially, thermally-vulcanizedvee-belt to its desired length, said vee-belt including a tensile memberof polyester material which contracts elastically with increasingtemperature, the steps of further thermally-vulcanizing thepartially-vulcanized belt while tensioned for a time sufficient tocoMpensate for the contraction caused by the initial partialthermal-vulcanization, and immediately placing the hot belt under atension caused by a load sufficient to prevent its contraction due tocooling and cause a slow expansion of the belt while still hot in orderto stretch the belt to bring it to its desired, length, and cooling thebelt to give a permanent set.
 3. A method according to claim 1, whereinthe vulcanization in the unstretched conditon takes place at 150* C. 4.In a method for producing a plurality of Vee-belts of uniform length,each belt including a tensile member of elastically-contractilepolyester produced as a condensation product from the reaction ofethylene glycol and a substance selected from terephthalic acid andderivatives thereof and which has been formed into a textile filament,each filament being liable to contract on heating, embedded in a vehicletire rubber mix, the improvement comprising the steps of subjecting eachsaid Vee-belt to an initial thermal vulcanization while the belts are inmotion around spaced pulleys and substantially free of tension,subjecting each said Vee-belt to further thermal vulcanization while thebelts are in motion around spaced pullys and under a tension such thaton completion of the further vulcanization the contraction produced bythe initial vulcanization has been offset, immediately thereafterplacing each hot belt under a load for its dimensions which issufficient to prevent contraction from the effects of cooling and allowa slow expansion of each belt while still hot, stretching each belt byan amount to bring it to the precise length which is desired, andimmediately cooling the belts to room temperature to stabilize them atthe said desired length.
 5. A method of forming a plurality of vee-beltsof uniform length, each belt composed of rubber material which encases atensile member of elastically-contractile polyester material having thephysical characteristic of contracting on heating, the method comprisingthe steps of: Subjecting said belts to a first thermal vulcanizing cyclein an unstressed conditon whereby said rubber material of each belt isvulcanized with its tensile member located therein in its desiredposition and each said belt shrinks to less than its original lengthfrom the contraction of its tensile member; Subjecting said belts to asecond thermal vulcanizing cycle while applying sufficient tensile forcethereto whereby said belts attain their original length in this secondcycle; While said belts are still hot, rotating same under a tensionsufficient to prevent their contraction while cooling and cause slowexpansion of the belts while still hot, and at the same time continuallymeasuring the length of said belts; and When said belts attain theiroriginal length, cooling said belts while continuing to rotate same;whereby each said belt has a permanent length within a tolerance of notgreater than 0.067 percent variance of its original length.